Framework Entry Points

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Framework Entry Points

The USB driver framework adds two entry points to normal device drivers:

void *probe(struct usb_device *dev, unsigned int interface, const struct usb_device_id *id_table); This entry point is called whenever a new device is attached to the bus. Then the device driver has to create a new instance of its internal data structures for the new device.
The dev argument specifies the device context, which contains pointers to all USB descriptors. The interface argument specifies the interface number. If a USB driver wants to bind itself to a particular device and interface it has to return a pointer. This pointer normally references the device driver's context structure.
Probing normally is done by checking the vendor and product identifications or the class and subclass definitions. If they match the interface number is compared with the ones supported by the driver. When probing is done class based it might be necessary to parse some more USB descriptors because the device properties can differ in a wide range.
A simple probe routine is shown in figure 5.

Figure 5: A simple probe function
$\begin{figure} \centering\index{probe function} \begin{verbatim} void *probe(s... ...tance context */ return context; }return NULL; }\end{verbatim}\end{figure}$
void disconnect(struct usb_device *dev, void *drv_context); This function is called whenever a device which was served by this driver is disconnected.
The argument dev specifies the device context and the driver_context returns a pointer to the previously registered driver_context of the probe function. After returning from the disconnect function the USB framework completly deallocates all data structures associated with this device. So especially the usb_device structure must not be used any longer by the usb driver.
A simple disconnect function is shown in figure 6.

Figure 6: A simple disconnect function
$\begin{figure} \centering\index{disconnect function} \begin{verbatim}static vo... ...e */ free_driver_resources(s);MOD_DEC_USE_COUNT; }\end{verbatim}\end{figure}$

**Figure 5:** A simple probe function
$\begin{figure} \centering\index{probe function} \begin{verbatim} void probe(s... ...tance context / return context; }return NULL; }\end{verbatim}\end{figure}$

**Figure 6:** A simple disconnect function
$\begin{figure} \centering\index{disconnect function} \begin{verbatim}static vo... ...e */ free_driver_resources(s);MOD_DEC_USE_COUNT; }\end{verbatim}\end{figure}$

Next: Framework Functions Up: The USB Device Driver Previous: Framework Data Structures Contents Index

Detlef Fliegl
2001-01-08